If your computer automatically installed service pack 3 from Microsoft you could try replacing your gnutella.net file.
Look in the "Connection" forums.
Bearshare and Limewire both work pretty much the same so it's quite often a similar thing that has made your application not work.
It's a bit strange that you can't play the songs that you've already downloaded (unless you're trying to play them with the bearshare built-in player, but you should be able to play them with Microsofts media player. If not, the solution I offered may not fix the problem.
Hope you have some good luck with finding a solution.